Strapi v25 sources is now hard to modify?

In my workplace, we have successfully incorporated strapi v.13.4 in our big project all thanks to the ability to patch the strapi sources (i know this is dangerous, but job requires it). With that in store, we could at least accommodate all sorts of custom requirements down to its internal working, as well as performing bug fixes are much doable.

However when we tried to experimenting with latest 4.25 (not v5) noticed that the sources are different now. Everything is just types definitions and index.js in dist folder (a transpiled version). Is there any way i could get its sources again like before ? is that going to be a big hassle with the new default typescript code base ?